We spent months obsessing over the thermal design of Umbrel Pro. Turns out when you fit an 8-core CPU, iGPU and 4 NVMe SSDs into a tiny form factor with toolless access, it's really hard to make it whisper quiet. Here's how we pulled it off 🧵

To achieve this form factor we use a double-sided PCB. CPU/GPU on top. Four M.2 SSD slots on the bottom. All cooled by a single low-profile fan. In a case small enough to sit on your desk.

However, the magnetic aluminium lid isn't just a lid. It's a massive heatsink. Lift it off to access your SSDs. Close it and the thermal pad makes direct contact with the top of all four drives.

But it gets better. We carved air intakes *inside* the structure of the lid.

Air is pulled into the lid vents > flows through its internal chambers > washes over the SSD chamber > gets directed through the holes behind the SSDs into the CPU chamber > exhausts out the back. One continuous airflow path. No dead zones.

So the aluminium lid is both passively cooled on the outside and actively cooled on the inside. While the top of the SSDs make direct contact with the lid and the bottom of the SSDs are cooled by active airflow. Every surface is working together to maximise cooling efficiency.

But hardware is only half the battle. Generic fan curves don't work when users install different SSDs with wildly different thermal limits. Umbrel Pro reads each SSD's self-reported thermal limit and dynamically generates a custom fan curve to keep them all in the safe zone.

But how do you manage 5 independent thermal zones (CPU/GPU + SSDs) with a single fan? We continuously sample all 5 sensors, calculate the required fan speed for each based on their specific curves, and apply the single highest value. One fan. Perfectly managing 5 components.

@stevenroose3 Not sure if you're a ZFS fan but if so you might also enjoy this